In an engine of a motorcycle, for example, an oil passage is conventionally provided inside a crankcase containing a crankshaft, inside a cylinder body disposed on the crankcase, and inside a cylinder head disposed above the crankcase. A transmission is disposed inside the crankcase. The transmission includes a main shaft and a drive shaft which rotate by receiving a driving force from the crankshaft. Oil is allowed to flow through the oil passage, thus lubricating the main shaft and the drive shaft. Japanese Patent No. 4717795 discloses an engine in which an oil pipe is assembled into the crankcase. The oil pipe is separate from the crankcase, and an oil passage through which oil flows is provided inside the oil pipe. The oil pipe is provided with an oil ejection hole from which oil is ejected toward the main shaft and the drive shaft.